Capsicum annuum L. plants are herbaceous plants of the family Solanaceae. The plant reaches about 0.5-1.5 meters (20-60 in). Single white flowers bear the pepper fruit which is green when unripe, changing principally to red, although some varieties may ripen to brown or purple. While the species can tolerate most climates, they are especially productive in warm and dry climates. Cultivated pepper plants of the species Capsicum annuum include different types of peppers, such as bell peppers, cayenne peppers, paprika, and jalapeños.
Tospoviruses are an important pathological threat to many plant species, causing considerable damage and yield loss worldwide (German et al. 1992, Ann Rev Phytopath V30: 315-348). Genes conferring or enhancing tospovirus resistance are therefore continuously sought after by plant breeders in order to develop resistant cultivars. The Sw-5 gene was transferred from Lycopersicon peruvianum into cultivated tomato, conferring resistance to Tospovirus serogroup I (e.g. TSWV, Tomato Spotted Wilt Virus) and serogroup II (e.g. GRSV and TCSV, Groundnut Ringspot Virus and Tomato Cholrotic Spot Virus, respectively).
Commercial sweet and hot pepper cultivars nowadays frequently contain the dominant resistance gene Tsw, which confers hypersensitive resistance to TSWV (but not to other Tospoviruses, such as GRSV or TCSV). The Tsw gene has been introgressed from lines of the species Capsicum chinense, PI152225, PI159236 (Black et al. 1991, Plant Disease 75: 863; Boiteux et al 1995, Theor. Appl. Genet. 90: 146-149; Costa et al. 1995, First Int. Symposium on Solanaceae for the Fresh Market, Mar. 28-31 1995, Malaga, Spain, Acta Hortic. 412: 523-532). Molecular markers for identifying and/or selecting Tsw have also been developed (Moury et al. 2000, Genome 43: 137-142) and Jahn et al. (2000, MPMI Vol 13: 673-682) have mapped the Tsw gene to chromosome 10 in Capsicum annuum. 
One drawback is that the TSWV resistance conferred by the Tsw gene is broken by high temperatures and also depends on plant age (young plants are more susceptible). Scientific evidence seems to suggest that the Tsw-resistance gene may work by impairing the long-distance transport of TSWV (see Rogero et al, Thrips and Tospoviruses: Proceedings of the 7th Int Symposium on Thysanoptera, pp 105-110).
An additional problem of the Tsw gene is that Tsw-resistance breaking strains of TSWV have been reported. The Tsw-resistance breaking strains are able to systemically infect plants carrying the dominant Tsw resistance gene. The first report of a resistance breaking strain, breaking the resistance of C. chinense, was in 1993 (Boiteaux et al. Plant Disease 77: 210). Later Moury et al. (1997, Euphytica 1994: 45-52) also found viral strains overcoming the Tsw resistance, although the virus isolates were not typed to assess if they were indeed TSWV isolates, rather than GRSV or TCSV isolates.
Roggero et al. (1999, Plant Disease Vol 83: p 965) found two field isolates of TSWV in Italy which overcame the Tsw-resistance in a pepper hybrid carrying the Tsw gene from PI15225. Serological assays confirmed that the virus isolates were TSWV strains, which were transmissible by the thrips vector Frankliniella occidentalis. In 2002 Roggero et al. reported further Tsw-resistance breaking strains in Italy (Plant Disease Vol 86: 950-954). All of the commercial pepper cultivars tested could be systemically infected by these resistance-breaking TSWV strains under experimental conditions. However, TSWV resistant tomato cultivars, carrying the Sw-5 gene, were not susceptible to Tsw-resistance breaking strains from pepper, showing that Sw-5 and Tsw have different characteristics (Roggero et al. 2002, supra). This was also confirmed by Jahn et al. (2000, supra).
In 2004, Margaria et al. (Plant Pathology Vol 53: p 794) reported the identification of Tsw-resistance breaking strains in the field in Spain (Almeria).
Margaria et al. 2007 (MPMI Vol 20: 547-558) studied the interaction between pepper plants carrying the dominant Tsw resistance gene and various natural TSWV strains, both wild type strains and strains which were able to break Tsw-resistance. Tsw-resistance breaking TSWV strains are designated by the superscript ‘RB’ in their study. One of these resistance breaking strains is Ve427RB isolated in 2003 from a pepper field in Almeria, Spain. In contrast to the wild type TSWV strains which caused only local damages on the inoculated pepper leaves of plants carrying the Tsw-gene, resistance breaking TSWV strains caused systemic infections, leading to, e.g., leaf chlorosis and yellow mottle throughout the infected plants. By using strains with reassortments between wild type (strain Br01wt) and RB strain genomes, Margaria et al. (2007, MPMI Vol 20: 547-558) were able to show that the avirulance determinant of the Tsw-resistance breaking strains is the NSs protein (nonstructural protein) found on the small RNA (S RNA). In resistance-breaking strains of this study, the NSs protein contained one or two mutations or deletions relative to the wild type NSs protein.
Although the dominant Tsw gene is still useful in providing resistance against TSWV to pepper varieties in many parts of the world, new sources of TSWV resistance are urgently needed, in order to minimize damage caused by new TSWV strains, especially by Tsw-resistance breaking strains.
It is an object of the invention to provide pepper plants comprising a new resistance gene, different from the Tsw-gene, which confers resistance against Tsw-resistance breaking strains, such as strains comprising mutations and/or deletions in the NSs protein. In one embodiment, the new resistance gene confers at least resistance against Tsw-resistance breaking strain Ve427RB. It is a further object of the invention to provide pepper plants comprising both the new resistance gene and the Tsw gene, i.e. plants which are resistant against wild type TSWV strains (pathotype P0) and against Tsw-resistance breaking strains (pathotype P1), at least against Ve427RB, but preferably also against other Tsw-resistance breaking strains (such as strains having one or more deletions and/or mutations in the NSs protein and/or strains which are capable of systemic infection of pepper plants carrying the Tsw-gene).